1. Field of the Invention
The present invention relates generally to muscle training machines and, more particularly, to weight adjusting devices for a muscle training machine.
2. Description of the Background Art
FIG. 11 shows a conventional muscle training machine. In use, the user stands in front of the muscle training machine 30 and pulls the handle 31 to lift the weight plates 33 through a string 32. The bottom weight plate 33 is fastened to a hanger bar 38 with a removable pin 41 which is inserted through horizontal aperture 40 into a latch hole 42 of the hanger bar 38.
The "weight reduction training method" is one of the most effective muscle training methods, wherein the weight is reduced stepwise by reducing the number of weight plates 33 in the course of exercise. In this training method, after the muscles are trained to the limit by pulling up and down the weight plates 33, the lowest weight plate 33 is removed by pulling out the pin 41 to reduce the weight, and the muscles are trained again to the limit with the reduced weight. Then, another weight plate 33 is removed for further muscle training. In this way, a weight plate 33 is removed each time the muscles are trained to the limit.
FIG. 9 shows a weight adjusting device 1 useful for such a muscle training machine as disclosed in Japanese patent application Kokai No. 1-308576. The weight adjusting device 1 includes one rectangular base 33 and four rectangular weight plates 31a-31d each having a central aperture for receiving a hanger bar 30 and a pair of apertures for receiving guiding posts 41. The hanger bar 30 is lifted by a hanging means 38.
A latch lever 32 is pivoted to the bottom face of each weight plate 31 for rotation in a horizontal plane. A lock lever 35 is pivoted to the front face of each weight plate 31 for rotation in a vertical plane. The lock levers 35 have a first shoulder 39 and a second shoulder 40 from which a release portion 36 extending downwardly. When it is in a lock position, the lock lever 35 locks the latch lever 32 in the latch position where the latch lever 32 engages the latch notch 34 of the hanger bar 30. When the release portion 36a abuts on the latch lever 32a, the latch lever 32b is released from the first shoulder 39 under the influence of a spring means (not shown) and hits the tip of the release portion 36b of the lock lever 35b.
In FIG. 10, an L-shaped interlocking arm 37 extends upwardly from the rear end portion of a latch lever 32 such that the upper portion contacts the lower portion of an interlocking arm 37 of the upper latch lever 32. When the lower latch lever 32 is turned counterclockwise toward the hanger bar 30, the interlocking arm 37 pushes the upper latch lever 32 for rotation. As a result, the upper latch lever 32 engages the latch notch 34 of the hanger bar 30 to fasten the weight plate 31 to the hanger bar. Thus, both the latch lever 32 are engaged with the hanger bar 30 by only a single manipulation of the lowest latch lever 32.
However, the amount of engagement between the latch lever 32 and the latch notch 34 is so small that the interlocking arm 37 is not sufficiently brought into contact with the interlocking arm 37 of the upper latch lever 32. Consequently, the rotation of the lower latch lever 32 is not fully transmitted to the upper latch lever 32. Thus, it is difficult to set two or more weight plates 31 on the hanger bar 30 by a single operation of the lowest latch lever 32.
Since the engagement of the latch lever 32 with the latch notch 34 is made on only one side of the hanger bar 30, the weight is offset from the center of gravity of the hanger bar 30. Consequently, the hanger bar 30 is inclined to one side, and the weight plates 31 make frictional contact with the guiding posts 41.
When the lower end of the release portion 36a hits the latch lever 32a by reducing the pulling force on the hanger string 38, the lock lever 35a is turned clockwise so that the latch lever 32b is released from the first shoulder 39 of the lock lever 35a. When the latch lever 32b hits the tip of the release portion 36b of the lock lever 35b, the lock lever 35b is turned clockwise to release the latch lever 32c from the latch notch 34. As a result, the two weight plates 31a and 31b are released simultaneously, making it difficult to practice the weight reduction training method.
Moreover, the bending angle of the L-shaped interlocking arms 37 depends on the length and thickness of the interlocking arms 37, making it complex to set the appropriate bending angle. When the surface of contact with the latch lever 32 varies, it is necessary to make fine adjustments to the bending angle during the manufacturing process, resulting in the increased manufacturing costs.